1. Field of the Disclosure
The present invention relates to positive gas delivery systems, such as pressure support systems and other ventilator (e.g., invasive) systems, and, more particularly, to a method for estimating leak in a gas delivery system, and a gas delivery system employing such a method.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in his or her esophagus. Such therapies are commonly referred to as non-invasive ventilation (NIV) therapies. For example, it is known to non-invasively deliver continuous positive airway pressure (CPAP) or variable airway pressure, which varies with the patient's respiratory cycle, to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), or congestive heart failure.
NIV therapies involve the placement of a patient interface device including a mask component on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal pillow/cushion having nasal prongs that are received within the patient's nares, a nasal/oral mask that covers the nose and mouth, or a full face mask that covers the patient's face. The patient interface device interfaces the ventilator or pressure support device with the airway of the patient through one or more delivery conduits (together commonly referred to as a patient circuit) so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient.
NIV using a single limb patient circuit has safely ventilated patients with respiratory insufficiency for over ten years and those with severe sleep apnea for over twenty years. In NIV, an accurate estimate of the patient flow is required for consistent and accurate volume delivery and for the ventilator to sense the patient's respiratory drive. The accuracy of the estimated patient flow is dependent on two things: (i) the accuracy and precision of the total flow signal (which is measured at the ventilator outlet and which is the composite of the patient flow and the flow caused by leaks (both intentional and unintentional) about the patient interface) and, (ii) the ability to model the leak flow as a function of one or more parameters such as pressure. Thus, one of the key technologies for effective NIV is the estimation of leak flow.